Numerical Simulation Of Axial Dispersion Coefficient And Flow Field In Pulsed Sieve-Plate Extraction Column

Pulsed-Sieve-Plate Extraction Column is a key device for spent fuel reprocessing technology, and it is always getting extensive attention and is being deeply investigated.In this paper, the CFD software Fluent is adopted to establish the model of fluid flow and tracer transfer in a pulsed sieve-plate extraction column, in order to obtain the calculation method of the axial diffusion coefficient of the continuous phase in a pulsed extraction column, in which the two phases coexist. Meantime, an actual pulsed-sieve-plate extraction column is used to verify the correctness of the simulation results. The extraction and mass transfer performance of pulsed-sieve-plate extraction column can be forecast on the basis of the simulation results. This paper adopts two-dimension axial symmetric grid to calculate the flow and mass transfer performances in the pulsed-sieve-plate extraction column.The experiment in this paper aims at acquiring the hydraulics parameters without considering the mass transfer between the two phases. Volume displacement method is used to measure the average holdup fraction of the discrete phase. As for volume fraction distribution of the discrete phase, the CFD simulation results show that:1) Pulse speed has a relatively larger influence on the discrete phase holdup fraction of the sieves plates near the lower part of the pulsed extraction column, resulting that this area is not stable. However, the holdup fraction of the upper area is well distributed. This phenomenon is further confirmed by the experiments.2) The influence of pulse on the holdup fraction increases from the top to the bottom of the pulsed extraction column and the average of the holdup fraction decreases. The average of the holdup fraction becomes nearly a constant at a certain height, and this region is the stable operation area of the sieve-plate extraction column.CFD simulation also shows that:1)The aqueous phase speed varies with the pulse speed and the organic phase speed changes not so obviously as the aqueous phase.2) The position at which the tracer's concentration reaches the highest varies with the pulse speed.3)By comparison of the tracers'holdup time, it is found that the measured concentration of tracer is close to the simulation result, however, the peak time deviate by 1 minute.On the basis of the axial dispersion model of the tracer dispersion, the least square method is adopted to process the tracer concentrations at the two sampling entrance, and the axial dispersion coefficient of the continuous phase is solved. According to the tracer concentration from the experiment results and simulation results by CFD, the axial dispersion coefficients of continuous phase are calculated.